Ack/nack transmission for multi-carrier operation with downlink assignment index

ABSTRACT

Techniques for acknowledging data transmissions in a multi-carrier wireless communication network are disclosed. In one aspect, a UE determines a number of acknowledgement/negative acknowledgement (ACK/NACK) bits for a data transmission on one more component carriers (CCs) based on information obtained from a grant. The grant may be a downlink grant or an uplink grant, and the information obtained may include a number of CCs scheduled for data transmission and/or identifiers of the scheduled CCs. The UE may determine the number of ACK/NACK bits for acknowledging the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC.

The present application claims priority to provisional U.S. Application Ser. No. 61/374,210, entitled “METHODS AND APPARATUS FOR ACK/NACK RELATED DESIGN FOR CARRIER AGGREGATION IN LTE-A NETWORKS,” filed Aug. 16, 2010, and incorporated herein by reference in its entirety.

BACKGROUND

I. Field

The present disclosure relates generally to communication and, more specifically, to techniques for supporting communication in a multi-carrier wireless communication network.

II. Background

Wireless communication networks are widely deployed to provide various communication content such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stations that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A wireless communication network may support operation on multiple component carriers (CCs). A CC may refer to a range of frequencies used for communication and may be associated with certain characteristics. For example, a CC may be associated with system information describing operation on the CC. A CC may also be referred to as a carrier, a cell, a serving cell, a frequency channel, etc.

SUMMARY

Techniques for acknowledging data transmissions in a multi-carrier wireless communication network are disclosed. In one aspect, a UE determines a number of acknowledgement/negative acknowledgement (ACK/NACK) bits to send for a data transmission on one more component carriers (CCs) based on information obtained from a grant. The grant may be a downlink grant or an uplink grant, and the information obtained may include a number of CCs scheduled for data transmission and/or identifiers of the scheduled CCs. The UE may determine the number of ACK/NACK bits for acknowledging the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC.

In one aspect, the UE may determine a transmission mode of each scheduled CC. The UE may determine the total number of ACK/NACK bits based on the transmission mode of each scheduled CC and the number of scheduled CCs. In another aspect, the UE may determine a number of transport blocks received on each scheduled CC and a total number of transport blocks received in the data transmission. The UE may use the total number of ACK/NACK bits and/or the total number of received transport blocks for various purposes including (i) determination of a transmit power for sending the ACK/NACK information on a PUCCH, (ii) determination of a number of resource elements for sending the ACK/NACK information on a PUSCH, (iii) determination of a number of bits available to multiplex channel state information (CSI) with the ACK/NACK information, and/or (iv) other purposes.

Various additional aspects and features of the disclosure are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication network.

FIG. 2 shows an exemplary frame structure for frequency division duplexing.

FIG. 3 shows an exemplary frame structure for time division duplexing.

FIGS. 4A and 4B show examples of carrier aggregation.

FIG. 5 shows aspects of data transmission on multiple CCs with HARQ.

FIG. 6 shows an example of determining an ACK/NACK bitwidth in a multi-carrier wireless communication network.

FIG. 7 shows an example of a downlink assignment index (DAI) for a multi-carrier wireless communication network.

FIG. 8 shows a process for sending ACK/NACK information.

FIG. 9 shows a process for receiving ACK/NACK information.

FIG. 10 shows an exemplary base station and an exemplary UE, which can perform the exemplary processes described herein.

FIG. 11 shows further aspects of base station and a UE according to the present disclosure.

DETAILED DESCRIPTION

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other wireless networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA), Time Division Synchronous CDMA (TD-SCDMA), and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi and Wi-Fi Direct), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in both frequency division duplexing (FDD) and time division duplexing (TDD), are new releases of UMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

FIG. 1 shows a wireless communication network 100, which may be an LTE network or some other wireless network. Wireless network 100 may include a number of evolved Node Bs (eNBs) 110 and other network entities. An eNB may be an entity that communicates with the UEs and may also be referred to as a Node B, a base station, an access point, etc. Each eNB may provide communication coverage for a particular geographic area and may support communication for the UEs located within the coverage area. To improve network capacity, the overall coverage area of an eNB may be partitioned into multiple (e.g., three) smaller areas. Each smaller area may be served by a respective eNB subsystem. In 3GPP, the term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area. In general, an eNB may support one or multiple (e.g., three) cells. The term “cell” may also refer to a carrier on which an eNB operates.

A network controller 130 may couple to a set of eNBs and provide coordination and control for these eNBs. Network controller 130 may communicate with the eNBs via a backhaul. The eNBs may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.

UEs 120 may be dispersed throughout the wireless network, and each UE may be stationary or mobile. A UE may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc. A UE may be a cellular phone, a smart phone, a tablet, a wireless communication device, a personal digital assistant (PDA), a wireless modem, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a netbook, a smartbook, etc. For clarity, some of the description below refers to UE 120 x and eNB 110 x, which may be one of the UEs and one of the eNBs in wireless network 100.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition a frequency spectrum into multiple (N_(FFT)) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (N_(FFT)) may be dependent on the system bandwidth. For example, the subcarrier spacing may be 15 kilohertz (KHz), and N_(FFT) may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.4, 3, 5, 10 or 20 megahertz (MHz), respectively.

Wireless network 100 may utilize FDD or TDD. For FDD, the downlink and uplink may be allocated separate frequency spectrum. Downlink transmissions may be sent on one frequency spectrum, and uplink transmissions may be sent on another frequency spectrum. For TDD, the downlink and uplink may share the same frequency spectrum, and downlink and uplink transmissions may be sent on the same frequency spectrum in different time intervals.

FIG. 2 shows an exemplary frame structure 200 for FDD in LTE. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown in FIG. 2) or six symbol periods for an extended cyclic prefix. The 2 L symbol periods in each subframe may be assigned indices of 0 through 2 L−1.

The available time frequency resources for each of the downlink and uplink may be partitioned into resource blocks. Each resource block may cover 12 subcarriers in one slot and may include a number of resource elements. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value.

FIG. 3 shows an exemplary frame structure 300 for TDD in LTE. Subframes 0 and 5 are used for the downlink, subframe 2 is used for the uplink, and subframes 3, 4, 7, 8 and 9 may each be used for the downlink or uplink. Subframe 1 includes a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). Subframe 6 may include only the DwPTS, or all three special fields, or a downlink subframe. LTE supports a number of uplink-downlink configurations for TDD. Each uplink-downlink configuration indicates whether each subframe is a downlink subframe, an uplink subframe, or a special subframe. There may be as many as nine downlink subframes to one uplink subframe in a radio frame.

As shown in FIGS. 2 and 3, a subframe for the downlink (i.e., a downlink subframe) may include a control region and a data region, which may be time division multiplexed (TDM). The control region may include the first Q symbol periods of the subframe, where Q may be equal to 1, 2, 3 or 4. Q may change from subframe to subframe and may be conveyed in the first symbol period of the subframe. The data region may include the remaining 2 L−Q symbol periods of the subframe and may carry data and/or other information for UEs.

An eNB may send downlink control information (DCI) on a physical downlink control channel (PDCCH) in the control region to a UE. The DCI may include a downlink grant, an uplink grant, power control information, etc. The eNB may send data and/or other information on a physical downlink shared channel (PDSCH) in the data region to the UE.

As shown in FIGS. 2 and 3, a subframe for the uplink (i.e., an uplink subframe) may include a control region and a data region, which may be frequency division multiplexed (FDM). The control region may include resource blocks near the two edges of the uplink spectrum (as shown in FIGS. 2 and 3) and may have a configurable size. The data region may include all resource blocks not included in the control region.

A UE may send uplink control information (UCI) to an eNB on a physical uplink control channel (PUCCH) in the control region of an uplink subframe. The UCI may include ACK/NACK information for a data transmission received on the downlink, channel state information (CSI), scheduling request (SR), etc. The UE may send data or data and UCI to the eNB on a physical uplink shared channel (PUSCH) in the data region of the uplink subframe. The UE may transmit only the PUCCH or only the PUSCH (and not both) in a subframe in order to maintain a single-carrier waveform, which may have a lower peak-to-average power ratio (PAPR). An uplink transmission may span both slots of a subframe and may hop across frequency.

Wireless network 100 may support multi-carrier operation on multiple CCs on the downlink and one or more CCs on the uplink. Operation on multiple CCs may be referred to as carrier aggregation. A CC for the downlink may be referred to as a downlink CC, and a CC for the uplink may be referred to as an uplink CC. An eNB may transmit data and DCI on one or more downlink CCs to a UE. A data transmission may include a transmission of one or more transport blocks (which may also be referred to as a PDSCH transmission) on each of at least one CC. For example, in a given subframe, the UE may receive multiple PDSCH transmissions on multiple configured CCs. The UE may transmit data and UCI to the eNB on one or more uplink CCs.

FIG. 4A shows an example of continuous carrier aggregation. In this example, M CCs are shown as adjacent to each other in frequency, where M may be any integer value. Each CC may have a bandwidth of 20 MHz or less and may be separately configured for a UE.

FIG. 4B shows an example of non-continuous carrier aggregation. In this example, M CCs are shown as separated from each other in frequency. Each non-contiguous CC may have a bandwidth of 20 MHz or less and may be separately configured for a UE.

With carrier aggregation, data and control information may be independently sent and received on each CC. This may be achieved, for example, by using (i) a separate inverse fast Fourier transform (IFFT) and a separate transmitter for each CC at a transmitting entity and (ii) a separate fast Fourier transform (FFT) and a separate receiver for each CC at a receiving entity. A transmission comprising up to M concurrent OFDM symbols or SC-FDMA symbols may be on up to M CCs in one symbol period. In another example, data and control information may be collectively sent and received on all CCs. This may be achieved by using (i) a single IFFT and a single transmitter for all M CCs at a transmitting entity and (ii) a single FFT and a single receiver for all M CCs at a receiving entity. A single OFDM symbol or SC-FDMA symbol may be transmitted on up to M CCs in one symbol period.

Wireless network 100 may support data transmission with hybrid automatic retransmission (HARQ) in order to improve reliability. For HARQ, a transmitter (e.g., an eNB) may send an initial transmission of a transport block and may send one or more additional transmissions of the transport block, if needed, until the transport block is decoded correctly by a receiver (e.g., a UE), or the maximum number of transmissions of the transport block has occurred, or some other termination condition is encountered. After each transmission of the transport block, the receiver may send an acknowledgement (ACK) if the transport block is decoded correctly, a negative acknowledgement (NACK) if the transport block is decoded in error, or a discontinuous transmission (DTX) if the transport block is missed. The transmitter may send another transmission of the transport block if a NACK or a DTX is received and may terminate transmission of the transport block if an ACK is received. A transport block may also be referred to as a packet, a codeword, a data block, etc.

FIG. 5 shows a scheme of transmitting DCI and data with HARQ on multiple (M) downlink CCs and transmitting UCI and data on one uplink CC. In this example, UE 120 x may periodically estimate the channel quality of different downlink CCs for eNB 110 x and may determine CSI for each downlink CC. The CSI may include channel quality indicator (CQI), precoding matrix indicator (PMI), rank indicator (RI), or a combination thereof. RI may indicate the number of layers or spatial channels to use for transmission of data. PMI may indicate a precoding matrix or vector to use for precoding data prior to transmission. CQI may indicate a channel quality for each transport block. UE 120 x may send CSI for each downlink CC to eNB 110 x periodically or when triggered.

eNB 110 x may use the CSI and/or other information to select UE 120 x for transmission of data, to schedule UE 120 x on one or more downlink CCs and/or the uplink CC, and to select one or more modulation and coding schemes (MCSs) for each downlink CC on which UE 120 x is scheduled. eNB 110 x may process (e.g., encode and modulate) one or more transport blocks for each scheduled CC based on the one or more MCSs selected for that CC. eNB 110 x may then send a transmission of one or more transport blocks (or a PDSCH transmission) on each scheduled CC to UE 120 x.

UE 120 x may receive and decode the transmission of one or more transport blocks on each scheduled CC in the plurality of configured CCs. For each configured CC, UE 120 x may determine whether a transmission of one or more transport blocks is detected and, when a transmission is detected, whether each transport block is decoded correctly or in error. UE 120 x may generate an ACK for each transport block decoded correctly and a NACK for each transport block decoded in error. UE 120 x may send ACK/NACK information comprising ACKs and/or NACKs for all transport blocks received on all M downlink CCs in a particular subframe.

eNB 110 x may receive the ACK/NACK information from UE 120 x, terminate transmission of each transport block for which an ACK is received, and send another transmission of each transport block for which a NACK is received. UE 120 x may also transmit data to eNB 110 x with the ACK/NACK information when there is data to send and when it has been scheduled for transmission of data on the uplink CC.

As shown in FIG. 5, eNB 110 x may send a downlink (DL) grant for a PDSCH transmission on a downlink CC to UE 120 x. The downlink grant may include various parameters for receiving and decoding the PDSCH transmission on the downlink CC. The downlink grant may be sent on the downlink CC on which the PDSCH transmission is sent or on another downlink CC. eNB 110 x may also send an uplink (UL) grant for a data transmission on the uplink CC by UE 120 x. The uplink grant may include various parameters for generating and sending the data transmission on a shared channel (e.g., PUSCH) of the uplink CC. The uplink grant may also include a CQI request. In this case, UE 120 x may send CSI with data on the PUSCH.

UE 120 x may transmit data and/or UCI, or neither, in a given subframe. The UCI may comprise only CSI, or only ACK/NACK, or both CSI and ACK/NACK. UE 120 x may be configured to periodically send CSI for each downlink CC of interest, which may be referred to as periodic CQI reporting. In this case, the UE may periodically send CSI reports in designated subframes determined by a schedule for periodic CSI reporting. Each CSI report may comprise CQI, PMI and/or RI for one or more downlink CCs. UE 120 x may also be requested to send CSI for one or more downlink CCs in any subframe, which may be referred to as aperiodic CSI reporting. This may be achieved by including a CSI request for one or more downlink CCs in an uplink grant.

eNB 110 x may send DCI (e.g., a downlink grant and/or an uplink grant) to UE 120 x on the PDCCH on a downlink CC. When UE 120 x is scheduled for a data transmission, eNB 110 x may send data on the PDSCH on a downlink CC. In a particular subframe, UE 120 x may send UCI (e.g., CSI and/or ACK/NACK) on the PUCCH on an uplink CC to eNB 110 x. Alternatively, when an uplink grant is received, UE 120 x may send only data or both data and UCI on the PUSCH on an uplink CC.

In general, UE 120 x may be configured with any number of downlink CCs and any number of uplink CCs for multi-carrier operation. For instance, UE 120 x may be configured with up to five downlink CCs and up to five uplink CCs for multi-carrier operation. In some examples, one downlink CC may be designated as a downlink primary CC (PCC), one uplink CC may be designated as an uplink PCC, and each remaining CC may be referred to as a secondary CC (SCC). eNB 110 x may send certain information (e.g., grants, ACK/NACK, etc.) on the downlink PCC to UE 120 x. UE 120 x may send certain information (e.g., CSI, ACK/NACK, scheduling request, etc.) on the uplink PCC to eNB 110 x.

Table 1 lists different types of CC referred to in the description herein.

TABLE 1 CC Type CC Type Description Configured CC A downlink CC that is configured for UE 120x. Activated CC A downlink CC that is configured and activated/enabled for use. Scheduled CC A downlink CC on which UE 120x is scheduled for data transmission. Detected CC A downlink CC on which UE 120x receives a data transmission.

UE 120 x may be semi-statically configured with M downlink CCs and one or more uplink CCs, e.g., via higher layer such as Radio Resource Control (RRC). In general, M may be any value greater than one. In one exemplary system, M may be less than or equal to five. Some or all of the configured CCs may be activated. An activated CC is a CC that a UE actively monitors on the downlink and/or actively transmits on the uplink. UE 120 x may not monitor a deactivated CC on the downlink, even though the CC is one of the configured CCs, which would result in power savings. UE 120 x may be scheduled for data transmission on all or a subset of the configured CCs in a given subframe. For dynamic scheduling, a downlink grant may be sent for a transmission of one or more transport blocks on each scheduled CC.

UE 120 x may detect a downlink grant on the PDCCH for a PDSCH transmission on a downlink CC (a “detected CC”). UE 120 x may receive the PDSCH transmission on the detected CC in accordance with the downlink grant. The downlink grant may be sent on the same downlink CC on which the associated PDSCH transmission is sent. In this case, the detected CC would be the downlink CC on which the downlink grant is received. The downlink grant may also be sent on one downlink CC, and the associated PDSCH transmission may be sent on a different downlink CC. For example, the downlink grant may include a carrier indication field (CIF) indicating the downlink CC on which the associated PDSCH transmission is sent. In that case, UE 120 x may identify the detected CC based on the CIF in the downlink grant. UE 120 x may detect some or all of the scheduled CCs, e.g., depending on whether UE 120 x missed any downlink grants sent to UE 120 x. UE 120 x may receive PDSCH transmissions on all detected CCs.

UE 120 x may be configured with M downlink CCs, and each downlink CC may be associated with a particular transmission mode in a set of supported transmission modes. Table 2 lists the transmission modes supported in LTE Release 9. Transmission modes 1, 2, 5, 6 and 7 support single-input single-output (SISO) or single-input multiple-output (SIMO) transmissions. Transmission modes 3, 4 and 8 support multiple-input multiple-output (MIMO) transmission.

TABLE 2 Transmission Modes Number of Transmission Transport Mode Blocks Description 1 1 Transmission from a single eNB antenna port 2 1 Transmit diversity 3 2 Open-loop spatial multiplexing 4 2 Closed-loop spatial multiplexing 5 1 Multi-user MIMO 6 1 Closed-loop rank 1 precoding 7 1 Transmission using UE-specific reference signal 8 2 Dual layer transmission

A transmission mode may be independently configured for each downlink CC. The M downlink CCs for UE 120 x may be configured with the same or different transmission modes.

One or more transport blocks may be sent on a downlink CC depending on the transmission mode configured for the downlink CC. In particular, one transport block may be sent on a downlink CC that is configured with transmission mode 1, 2, 5, 6 or 7, and two transport blocks may be sent on a downlink CC that is configured with transmission mode 3, 4 or 8. UE 120 x may generate one ACK/NACK bit for each transport block. For example, one ACK/NACK bit may used to acknowledge a data transmission on a CC configured in transmission mode 1, 2, 5, 6 or 7 and two ACK/NACK bits may be used to acknowledge a data transmission on a CC configured in transmission mode 3, 4 or 8.

The number of ACK/NACK bits for acknowledging a transmission of one or more transport blocks on a downlink CC may also be dependent on a DCI format of a corresponding downlink grant. LTE supports a number of DCI formats. DCI format 1, 1A, 1B, 1C or 1D may be used to send a downlink grant for a transmission of one transport block and may thus be associated with one ACK/NACK bit. DCI formats 2, 2A or 2B may be used to send a downlink grant for a transmission of two transport blocks and may thus be associated with two ACK/NACK bits. A DCI format of a downlink grant may be associated with a particular number of transport blocks to send on a downlink CC, which may be different from (e.g., fewer than) the number of transport blocks associated with a transmission mode configured for the downlink CC. For example, CCj may be configured with a transmission mode supporting two transport blocks but may be scheduled with a downlink grant having a DCI format used with one transport block. In that case, eNB 110 x may send one transport block on CCx and UE 120 x may generate one bit of ACK/NACK information to acknowledge the data transmission on CCj.

In one example, UE 120 x may be configured with five downlink CCs for multi-carrier operation in FDD. In this case, in a given subframe, eNB 110 x may send up to ten transport blocks on up to five downlink CCs, with up to two transport blocks per downlink CC. Up to ten ACK/NACK bits may be obtained for up to ten transport blocks, one ACK/NACK bit for each transport block (up to 12 ACK/NACK bits may be obtained if DTX is explicitly signaled). UE 120 x may thus have N ACK/NACK bits for a data transmission over M configured downlink CCs, where 1≦M≦N≦10.

According to the present disclosure, techniques for determining the number of ACK/NACK bits for a data transmission on M downlink CCs in a multi-carrier wireless communication network are described. The number of ACK/NACK bits for acknowledging a data transmission may be determined in different manners depending on the availability of certain information. The number of ACK/NACK bits, in turn, may be used to control transmission of ACK/NACK information. In one aspect, a downlink assignment index (DAI) may be used to facilitate determination of the number of ACK/NACK bits for a data transmission on M downlink CCs. A DAI may be included in a downlink grant and may indicate the number of downlink CCs scheduled and/or may provide an indication of which downlink CCs are scheduled. The DAI may help UE 120 x to detect missing downlink grants, facilitate more efficient ACK/NACK feedback, and/or provide other advantages.

The total number of ACK/NACK bits for M configured CCs may be referred to as the ACK/NACK bitwidth, the ACK/NACK payload size, etc. The ACK/NACK bitwidth may be dependent on whether ACK/NACK bits for different downlink CCs are ordered or non-ordered. The use of ordered or non-ordered feedback may be configured for UE 120 x. For the non-ordered case, ACK/NACK bits for the M configured CCs may be concatenated in a predetermined order, e.g., based on an index of each downlink CC. For the ordered case, ACK/NACK bits for the M configured CCs may be concatenated by first considering ACK/NACK bits for the scheduled CCs and then considering ACK/NACK bits for the remaining CCs.

FIG. 6 shows an example of determining ACK/NACK bitwidth for the ordered and non-ordered cases. In this example, UE 120 x is configured with five downlink CCs (CC1-CC5). CC2 and CC5 are associated with 1-bit ACK/NACK feedback (e.g., based on transmission mode and DCI format as previously discussed). CC1, CC3 and CC4 are associated with 2-bit ACK/NACK feedback. Only CC2, CC3 and CC4 are scheduled in a particular subframe. A set of bits to be encoded and sent as ACK/NACK feedback may be determined as follows:

-   -   Non-ordered case: ‘00’ (CC1)+1 bit (CC2)+2 bits (CC3)+2 bits         (CC4)+‘0’(CC5)+zeros, or     -   Ordered case: 1 bit (CC2)+2 bits (CC3)+2 bits (CC4)+zeros.

ACK/NACK information may be sent on the PUCCH or PUSCH in a fixed payload size. In this case, zero padding with a sufficient number of zeros may be performed to obtain a set of bits of the proper payload size.

The non-ordered case may result in simpler operation since one or two ACK/NACK bits for each configured CC may be readily obtained from the ACK/NACK feedback based on the CC index and the number of ACK/NACK bits for each configured CC. However, the ordered case may have better efficiency since the ACK/NACK bits for the scheduled CCs are placed first and may thus result in fewer bits being used for ACK/NACK feedback. In some examples, CSI and/or other information may be multiplexed in the remaining bits of the payload after ACK/NACK information for the scheduled carriers is added.

Table 3 lists three DAI schemes for multi-carrier operation according to the present disclosure. In the first scheme, a DAI is not included in downlink grants. In the second and third schemes, a DAI is supported and conveys different information. Determination of ACK/NACK bitwidth based on each of the three schemes is described below.

TABLE 3 DAI Schemes Scheme Description First No DAI Downlink grant does not include DAI. Scheme Second DAI indicates Downlink grant includes DAI indicating Scheme number of number of downlink CCs scheduled in scheduled CCs a subframe. Third DAI identifies Downlink grant includes DAI indicating Scheme scheduled CCs number of downlink CCs and which downlink CCs are scheduled in a subframe.

In the second scheme, the DAI indicates the number downlink CCs being scheduled and may be set to a value within a range of 1 to M−1. In one example, the DAI may have a variable width, which may be dependent on M. For example, the DAI may include one bit for M=2, two bits for M=3 or 4, or three bits for M=5. In another example, the DAI may have a fixed width (e.g., of three bits) that is independent of M. The DAI may be included in a downlink grant for each scheduled CC or for only certain scheduled CCs.

In the third scheme, the DAI indicates the number of downlink CCs being scheduled as well as which downlink CCs are scheduled. The DAI may be included in a downlink grant for a scheduled CC and may indicate which other downlink CCs (if any) are also scheduled. The DAI may be defined in different manners for the third scheme.

In a first variation of the third scheme, the DAI may have a variable width that is dependent on M. The number of bits used for the DAI may be smaller than the number of configured CCs. For example, if M=1, then the DAI may be omitted. If M=2, then the DAI may comprise one bit and may be set to (i) a first value (e.g., ‘0’) to indicate one downlink CC being scheduled, which is the downlink CC associated with the downlink grant including the DAI, or (ii) a second value (e.g., ‘1’) to indicate two downlink CCs being scheduled. If M=3, then the DAI may comprise two bits and may be set to (i) a first value (e.g., ‘00’) to indicate one downlink CC being scheduled, (ii) a second value (e.g., ‘01’) to indicate a first remaining downlink CC also being scheduled, (iii) a third value (e.g., ‘10’) to indicate a second remaining downlink CC also being scheduled, or (iv) a fourth value (e.g., ‘11’) to indicate all three downlink CCs being scheduled.

To further illustrate this design, consider the case of three configured CCs (CCx, CCy and CCz). The eNB may set the DAI in a downlink grant for CCx to the second value to indicate that CCy is scheduled, or to the third value to indicate that CCz is scheduled. If M=4, a 3-bit DAI may be utilized. The DAI may be set to (i) a first value to indicate one downlink CC being scheduled, (ii) a second, a third, or a fourth value to indicate one other downlink CC also being scheduled among the three remaining downlink CCs, (iii) a fifth, a sixth, or a seventh value to indicate two other downlink CCs also being scheduled among the three remaining downlink CCs, or (iv) an eight value to indicate all four downlink CCs being scheduled.

Continuing with the example, a 4-bit DAI may be utilized when M=5. The DAI may be set to (i) a first value to indicate one downlink CC being scheduled, (ii) a value within the 2nd through 5th value to indicate one other downlink CC also being scheduled among the four remaining downlink CCs, (iii) a value within the 6th through 11th value to indicate two other downlink CCs also being scheduled among the four remaining downlink CCs, (iv) a value within the 12th through 14th value to indicate three other downlink CCs also being scheduled among the four remaining downlink CCs, or (v) a 15th value to indicate all five downlink CCs being scheduled. When the variable width DAI of the third scheme is utilized, UE 120 x may be able to determine how many downlink CCs and which downlink CCs are scheduled based on the DAI in one downlink grant for one scheduled CC.

In another variation of the third scheme, the DAI may comprise a bitmap of M−1 bits, with one bit for each remaining downlink CC (not including the downlink CC on which the PDCCH is received). The bit for each remaining downlink CC may be set to a first value (e.g., ‘0’) to indicate the downlink CC is not scheduled or to a second value (e.g., ‘1’) to indicate the downlink CC is scheduled. The number of downlink CCs being scheduled may be equal to 1 (for the downlink CC associated with a downlink grant carrying the DAI) plus the number of ones in the bitmap.

FIG. 7 shows an example of the DAI for the bitmap variation of the third scheme. In this example, the DAI is included in a downlink grant for a PDSCH transmission on downlink CC2 and comprises a bitmap of M−1 bits for M−1 other downlink CCs. The bit for CC1 is set to ‘0’ to indicate CC1 not being scheduled, the bit for CC3 is set to ‘1’ to indicate CC3 being scheduled, etc. UE 120 x may receive the DAI in a downlink grant for a PDSCH transmission on one scheduled CC. Based on the DAI, UE 120 x can determine all scheduled CCs based on the DAI in the received downlink grant, even if it does not detect the downlink grants for all of the other scheduled CCs.

In another variation of the third scheme, the DAI may comprise a limited number of bits, and only some scheduled CCs may be identified by the DAI. For example, the DAI may comprise two bits (instead of M−1 bits) even when more than two downlink CCs are scheduled. In this variation, the downlink PCC may be given higher priority than the downlink SCCs. For M=3, the DAI can identify each downlink CC that is scheduled, as described above. For M=4, the DAI in a downlink grant for the PCC may include one bit covering two SCCs and another bit covering the last SCC. The DAI in a downlink grant for an SCC may include one bit covering the PCC and another bit covering the other two SCCs. For M=5, the DAI in a downlink grant for the PCC may include one bit covering two SCCs and another bit covering the last two SCCs. The DAI in a downlink grant for an SCC may include one bit covering the PCC and another bit covering the other three SCCs. With this variation, two or more entries may share the same DAI value. For example, the same DAI value (e.g., ‘00’) may be used for the case of one scheduled CC and another case of four scheduled CCs, since the probability of confusion between these two cases may be small. This may allow for a tradeoff between overhead and ambiguity in the information provided by the DAI.

As described herein, further variations of the DAI may also utilized with the second and third schemes. In addition, the DAI may convey different information depending upon the CC configuration for a particular UE such that different DAI schemes may be utilized with different CC configurations or in support of different UEs.

A DAI indicating the number of scheduled CCs and/or identifying the scheduled CCs may be sent in various manners. In one example, the DAI may be included in each downlink grant sent on the PDCCH for each scheduled CC. In another example, the DAI may be included only in downlink grants for the downlink PCC. In yet another example, the DAI may be included in one or more downlink grants for one or more designated CCs, e.g., the first and last CCs. Additionally or alternatively, a DAI for downlink data transmission may be included in an uplink grant sent on the PDCCH. This design may provide additional protection against missed detection of the PDCCH by a UE.

The ACK/NACK bitwidth for M configured CCs may be determined in various manners for the three schemes listed in Table 3. Some exemplary designs of determining the ACK/NACK bitwidth are described below.

For the first scheme with no DAI, an exemplary ACK/NACK bitwidth for M configured CCs may be determined as follows:

$\begin{matrix} {{n_{HARQ} = {\sum\limits_{C \in {{Configured}\_ {Set}}}n_{C}}},} & {{Eq}\mspace{14mu} (1)} \end{matrix}$

where n_(C) is the number of ACK/NACK bits for downlink CC C,

-   -   n_(HARQ) is the total number of ACK/NACK bits for M configured         CCs, and Configured_Set denotes a set of configured CCs.

n_(HARQ) is the ACK/NACK bitwidth for the M configured CCs. n_(HARQ) in equation (1) may be the same for both the ordered and non-ordered cases.

In another design, the ACK/NACK bitwidth for cases where no DAI is provided may be determined as follows:

$\begin{matrix} {{n_{HARQ} = {\sum\limits_{C \in {{Activated}\_ {Set}}}n_{C}}},} & {{Eq}\mspace{14mu} (2)} \end{matrix}$

where Activated_Set denotes a set of activated CCs. The set of activated CCs may include all or a subset of the M configured CCs.

In yet another design, in the absence of DAI, the ACK/NACK bitwidth may be determined as follows:

$\begin{matrix} {{n_{HARQ} = {\sum\limits_{C \in {{Detected}\_ {Set}}}n_{C}}},} & {{Eq}\mspace{14mu} (3)} \end{matrix}$

where Detected_Set denotes a set of detected CCs. The set of detected CCs may include all or a subset of the M configured CCs. Detected CCs may be determined as described above.

As shown in equation (3), when the detected CCs are known from the detection of downlink grants, the ACK/NACK bitwidth may be determined based on the ACK/NACK bits for only the detected CCs. This may result in a smaller and more accurate ACK/NACK bitwidth.

n_(C) in equations (1) to (3) may be defined in the same manner or different manners. For example, n_(C) in equation (1) may be determined based on a transmission mode of each CC in the configured set, whereas n_(C) in equation (3) may be determined based on a DCI format of a downlink grant for the CCs in the detected set.

For the second scheme with DAI indicating the number of scheduled CCs, the ACK/NACK bitwidth for M configured CCs may be determined differently for the ordered and non-ordered cases described above. In one example of the non-ordered case, ACK/NACK bitwidth may be determined based on the configured CCs, as shown in equation (1). Although only a subset of the M configured CCs may be scheduled, the DAI may not indicate which particular downlink CCs are scheduled. Hence, the UE may determined an ACK/NACK bitwidth based on a number of ACK/NACK bits for all M configured CCs.

When ordered feedback is used with the second scheme, ACK/NACK bitwidth may be determined in different manners. In one example, the ACK/NACK bitwidth may be determined as follows:

$\begin{matrix} {n_{HARQ} = \left\{ \begin{matrix} n_{C} & {{{for}\mspace{14mu} {DAI}} = 1} \\ {{DAI}*{\max \left( n_{C} \right)}} & {{{for}\mspace{14mu} 1} < {DAI} < M} \\ {\sum\limits_{C \in {{Configured}\_ {Set}}}n_{C}} & {{{for}\mspace{14mu} {DAI}} = M} \end{matrix} \right.} & {{Eq}\mspace{14mu} (4)} \end{matrix}$

In equation (4), the ACK/NACK bitwidth varies according to the number of scheduled CCs and may be equal to the number of ACK/NACK bits for the CC on which PDCCH is transmitted when one downlink CC is scheduled (with DAI=1). The ACK/NACK bitwidth may be equal to the total number of ACK/NACK bits for all M configured CCs if all configured CCs are scheduled (with DAI=M). The ACK/NACK bitwidth and may be equal to the number of scheduled CCs times the maximum number of ACK/NACK bits per scheduled CC if two to M−1 downlink CCs are scheduled. Since DAI*max(n_(C)) may be larger than Σn_(C), n_(HARQ) may be limited to Σn_(C).

In another example, when ordered feedback is used with the second scheme, the ACK/NACK bitwidth may be determined as follows:

$\begin{matrix} {\mspace{79mu} {n_{HARQ} = \left\{ \begin{matrix} n_{C} & {{{for}\mspace{14mu} {DAI}} = 1} \\ {{DAI}*{\max \left( n_{C} \right)}} & {{{for}\mspace{14mu} 1} < {DAI} < M} \\ {\sum\limits_{C \in {{Configured}\_ {Set}}}n_{C}} & {{{for}\mspace{14mu} {DAI}} = M} \end{matrix} \right.}} & {{Eq}\mspace{14mu} (5)} \\ {n_{X} = {{\max \left\{ {n_{1},\ldots \mspace{14mu},{\cdot n_{M - {DAI} + 1}}} \right\}} + {\max \left\{ {n_{2},\ldots \mspace{14mu},{\cdot n_{M - {DAI} + 2}}} \right\}} + \ldots + {\max \left\{ {n_{DAI},\ldots \mspace{14mu},{\cdot n_{M}}} \right\}}}} & {{Eq}\mspace{14mu} (6)} \end{matrix}$

In equation (6), for a given DAI value, the first scheduled CC is among downlink CCs 1 through M−DAI+1, the second scheduled CC is among downlink CCs 2 through M−DAI+2, and so on, and the last scheduled CC is among downlink CCs DAI to M. This observation is exploited in equation (6) to possibly reduce the ACK/NACK bitwidth. Since n_(X) may be larger than Σn_(C), n_(HARQ) may be limited to Σn_(C). For example, UE 120 x may be configured with five downlink CCs associated with 1, 2, 1, 2 and 1 ACK/NACK bits based on the transmission modes configured for these downlink CCs. In this example, Σn_(C) is equal to 7 bits. If four downlink CCs are scheduled and DAI=4, then n_(X) is equal to 8 and is larger than Σn_(C). In this case, n_(HARQ) may be limited to 7. Conversely, if three downlink CCs are scheduled and DAI=3, then n_(X) is equal to 6 and is smaller than Σn_(C). In this case, n_(HARQ) is equal to 6. For the case of two downlink CCs, n_(HARQ) may be set to Σn_(C).

For the third scheme in which a DAI identifies both the number and identity of the scheduled CCs, the ACK/NACK bitwidth for M configured CCs may be determined as follows:

$\begin{matrix} {{n_{HARQ} = {\sum\limits_{C \in {{Scheduled}\_ {Set}}}n_{C}}},} & {{Eq}\mspace{14mu} (7)} \end{matrix}$

where Scheduled_Set denotes a set of scheduled CCs.

As shown in equation (7), when the scheduled CCs are known from the DAI, the ACK/NACK bitwidth may be determined based on the ACK/NACK bits for only the scheduled CCs. For example, the number of ACK/NACK bits for each scheduled CC may be determined based on (i) the transmission mode configured for the scheduled CC or (ii) the DCI format of a downlink grant for the scheduled CC. This would increase efficiency by facilitating a more accurate determination of the ACK/NACK bitwidth.

Table 4 summarizes the determination of ACK/NACK bitwidth for the three schemes listed in Table 3.

TABLE 4 ACK/NACK Bitwidth Determination Scheme Non-ordered Case Ordered Case Comments No DAI Σn_(C) over Same as non- Fixed ACK/NACK configured CCs ordered case overhead if sum over or detected CCs configured CCs. DAI Σn_(C) over Equation (4) or Ordered ACK/NACK indicates configured CCs Equations feedback may be more number of (5) & (6) efficient. scheduled CCs DAI Σn_(C) over Same as non- Minimum ACK/NACK identifies scheduled CCs ordered case overhead. scheduled CCs

In one example of operation, which may be applicable for all three schemes listed in Table 3, UE 120 x may determine the total number of transport blocks received on the M configured CC. UE 120 x may detect for downlink grants intended for UE 120 x and may determine the DCI format of each detected downlink grant. UE 120 x may receive one transport block on each downlink CC associated with a downlink grant having a DCI format supporting one transport block. UE 120 x may receive two transport blocks on each downlink CC associated with a downlink grant having a DCI format supporting two transport blocks. UE 120 x may determine the total number of transport blocks received on all configured CCs as follows:

$\begin{matrix} {{n_{TB} = {\sum\limits_{C \in {{Detected}\_ {Set}}}n_{{TB},C}}},} & {{Eq}\mspace{14mu} (8)} \end{matrix}$

where n_(TB,C) is the number of transport blocks received on downlink CC C, and

n_(TB) is the total number of transport blocks received on all configured CCs.

The total number of transport blocks received on all configured CCs (n_(TB)) may be referred to as a total transport block count. UE 120 x may determine the ACK/NACK bitwidth based on the total transport block count, e.g., one ACK/NACK bit for each received transport block, so that n_(HARQ)=n_(TB). The number of transport blocks received on each downlink CC may be equal to or less than the number of transport blocks for a transmission mode configured for that downlink CC. Hence, the total transport block count determined based on detected downlink grants may be equal to or less than the ACK/NACK bitwidth determined based on transmission modes of the configured CCs or detected CCs. The ACK/NACK bitwidth determined based on transmission modes may be considered as (i) the maximum possible number of ACK/NACK bits for M configured CCs, or (ii) the total number of bits available to send ACK/NACK information for the M configured CCs. The total transport block count may be considered as the actual number of ACK/NACK bits to send for the M configured CCs.

UE 120 x may send ACK/NACK information for M configured CCs on either the PUCCH or PUSCH in a given subframe, e.g., depending on whether UE 120 x is also scheduled for data transmission on the uplink in the subframe. The ACK/NACK bitwidth and/or the total transport block count may be used for various purposes such as one or more of the following:

-   -   Power control of ACK/NACK information sent on the PUCCH,     -   Determination of a number of resource elements for sending         ACK/NACK information on the PUSCH,     -   Determination of an ACK/NACK feedback scheme for sending         ACK/NACK information on the PUCCH,     -   Determination of a code rate and/or a coding scheme for sending         ACK/NACK information on the PUCCH or PUSCH, and     -   Determination of available bits for sending CSI and/or other         information with ACK/NACK information on the PUCCH or PUSCH.

A multi-carrier UE may also perform power control for the PUCCH based on the ACK/NACK bitwidth or the total transport block count. In general, the signal-to-noise ratio (SNR) needed to reliably receive an ACK/NACK transmission may be dependent on the ACK/NACK bitwidth, or the number of ACK/NACK bits to send. The ACK/NACK bitwidth may, in turn, be dependent on the number of scheduled CCs. Since the required SNR may vary by more than 3 dB, e.g., for one scheduled CC versus five scheduled CCs, accurate determination of ACK/NACK bitwidth is important for efficient operation in a multi-carrier network.

The transmit power to use to send ACK/NACK information and possibly CSI on the PUCCH may be determined as follows:

P _(PUCCH) =f{h(n _(CSI) ,n _(HARQ))},  Eq (9)

where

n_(CSI) is the number of CSI bits to send with ACK/NACK information,

h(.) is a predefined function described in LTE,

f(.) is another predefined function described in LTE, and

P_(PUCCH) is the transmit power for the PUCCH.

As shown in equation (9), the transmit power of the PUCCH may be dependent on the number of ACK/NACK bits to send, or ACK/NACK bitwidth. The ACK/NACK bitwidth for power control of the PUCCH may be determined in various manners. In a first example, which may be referred to as a slow option, ACK/NACK bitwidth may be determined based on the configured CCs for UE 120 x, which may be computed as shown in equation (1) for the first scheme. In a second example, which may be referred to as a medium option, the ACK/NACK bitwidth may be determined based on the activated CCs for UE 120 x, which may be computed as shown in equation (2) for the first scheme. In a third example, which may be referred to as a fast option, the ACK/NACK bitwidth may be determined based on the detected CCs carrying data on the PDSCH, which may be computed as shown in equation (3) for the first scheme.

Other approaches may also include determining ACK/NACK bitwidth based on the scheduled CCs. For example, ACK/NACK bitwidth may be determined over the set of scheduled CCs as when the DAI identifies both number and identity of each scheduled CC, e.g., as shown in equation (7). Alternatively, the ACK/NACK bitwidth may be determined based on the total number of transport blocks received on the M configured CCs, e.g., as shown in equation (8). The ACK/NACK bitwidth may also be depend upon whether an ordered or non-order feedback configuration is utilized as previously discussed.

The slow and medium options may result in “over” power control since UE 120 x may be scheduled on fewer downlink CCs than the configured CCs. UE 120 x may then use higher transmit power for the PUCCH than necessary. The fast option may result in “under” power control since UE 120 x may miss detecting downlink grants on the PDCCH for some scheduled CCs. UE 120 x may then use less transmit power for the PUCCH than necessary. However, the likelihood of missing detection of downlink grants may be low (e.g., typically around 1% for each downlink CC). Hence, the under power control issue may not be severe.

Power control of the PUCCH can be performed by eNB 110 x to mitigate the potential for a power control mismatch as described above. For the slow and medium options, eNB 110 x may determine a power down command based on the difference between the number of scheduled CCs and the number of configured or activated CCs. For the fast option, eNB 110 x may determine a power up command based on the difference between an estimate of the number of detected CCs by UE 120 x (which is unknown to eNB 110 x) and the number of scheduled CCs (which is known to eNB 110 x). For all options, eNB 110 x may send a power control command (which may be a power down command or a power up command) to UE 120 x. The power control command may be sent via embedded information in a downlink grant, or via group power control in DCI formats 3/3A, or via some other mechanism. UE 120 x may adjust its computed transmit power for the PUCCH based on the power control command.

For transmissions on PUSCH, the number of resource elements to use to send ACK/NACK information (which may be referred to as the required number of PUSCH resource elements) may be determined based on the ACK/NACK bitwidth or the total transport block count. In one example, UE 120 x may determine a number of PUSCH resource elements based on the ACK/NACK bitwidth for the configured CCs, which may be computed as shown in equation (1) for the no-DAI case. In a second example, UE 120 x may determine the number of PUSCH resource elements for acknowledging a data transmission based on the ACK/NACK bitwidth for the activated CCs, which may be computed as shown in equation (2) for the no-DAI case. In a third example, UE 120 x may determine the number of PUSCH resource elements based on the ACK/NACK bitwidth for the detected CCs, which may be computed as shown in equation (3) for the no-DAI case. In other examples, UE 120 x may determine the number of PUSCH resource elements based on (i) the ACK/NACK bitwidth for the scheduled CCs, which may be determined as shown in equation (7) for the third scheme, or (ii) the total number of transport blocks received on the M configured CCs, which may be determined as shown in equation (8).

In each of the above examples, the number of PUSCH resource elements for acknowledging a data transmission may be reserved or set aside from among all resource elements available on the PUSCH. UE 120 x may send ACK/NACK information on the reserved resource elements on the PUSCH. Data and/or other information may be sent on the remaining resource elements on the PUSCH. eNB 110 x may configure UE 120 x for a particular resource utilization scheme on the PUSCH to avoid misalignment.

When UE 120 x determines that ACK/NACK information is sent on the PUCCH, ACK/NACK feedback scheme may be determined based on the ACK/NACK bitwidth or the total transport block count. For example, up to two bits of ACK/NACK information may be sent on the PUCCH based on PUCCH format 1 a or 1 b. PUCCH format 1 a supports transmission of one ACK/NACK bit on the PUCCH and may be used when one downlink CC is scheduled. PUCCH format 1 b supports transmission of two ACK/NACK bits on the PUCCH and may be used when two transport blocks are scheduled on one downlink CC or one transport block is scheduled on each of two downlink CCs.

Up to four bits of ACK/NACK information may be sent on the PUCCH based on PUCCH format 1 b and channel selection. In this example, two signaling bits, b₀ and b₁, may be sent on one of multiple PUCCH resources available for use by UE 120 x. The values of bits b₀ and b₁ as well as the selected PUCCH resource may be determined based on the ACK/NACK information.

When UE 120 x is configured for PUCCH format 3, which utilizes DFT-spread OFDM (DFT-S-OFDM), more than four bits of ACK/NACK information may be sent on the PUCCH. For PUCCH format 3, n_(HARQ) bits of ACK/NACK information may be transformed to the frequency domain based on a DFT and mapped to resource elements in one or more resource blocks used for ACK/NACK transmission. SC-FDMA symbols may be generated based on the mapped symbols.

PUCCH format 3 may be used to send ACK/NACK information regardless of the number of downlink CCs. This approach allows the same PUCCH format to be used irrespective of the number of configured CCs or scheduled CCs. For example, eNB 110 x may process the ACK/NACK information based on one PUCCH format (instead of having to perform blind detection for different PUCCH formats). Additionally, using the additional payload available with PUCCH format 3, UE 120 x can multiplex CSI and/or other information with ACK/NACK information. PUCCH format 3 may also be used to send only CSI, which may simplify operation of eNB 110 x to detect for CSI and/or ACK/NACK information from UE 120 x.

All or a subset of the designs described above may be used to send ACK/NACK information on the PUCCH. For example, PUCCH format 1 a/1 b and PUCCH format 3 may be used as appropriate. The ACK/NACK bitwidth for selecting a suitable ACK/NACK feedback scheme may be determined based on the configured CCs, the activated CCs, the detected CCs, or the scheduled CCs.

UE 120 x can select a code rate and/or a coding scheme for ACK/NACK information based on the ACK/NACK bitwidth or the total transport block count. The ACK/NACK information may be encoded based on a block code (e.g., a Reed-Muller code) of a particular code rate to obtain coded data. The coded data may be further processed and sent on the PUCCH or PUSCH. Selection of a suitable code rate may be especially relevant for ACK/NACK information sent on the PUCCH based on PUCCH format 3 as well as for ACK/NACK information multiplexed with data on the PUSCH.

As described above, the number of bits of ACK/NACK information (n_(HARQ)) may be variable and dependent on the ACK/NACK bitwidth. The number of bits of coded data (n_(PAYLOAD)), on the other hand, may be fixed and dependent on the available payload for ACK/NACK information on the PUCCH or PUSCH. The code rate may be selected based on n_(HARQ) and n_(PAYLOAD) so that the coded data can be sent in the available payload on the PUCCH or PUSCH. The code rate may be determined based on the ACK/NACK bitwidth for the configured CCs, the activated CCs, the detected CCs, or the scheduled CCs. Selecting the code rate based on the ACK/NACK bitwidth for the configured CCs may ensure that eNB 110 x and UE 120 x will both use the same code rate. Selecting the code rate based on the ACK/NACK bitwidth for the activated CCs or the detected CCs may provide better performance with an increased possibility of misalignment between the code rate determined by eNB 110 x and the code rate determined by UE 120 x. In one example, eNB 110 x performs decoding for different possible code rates to address possible misalignments. Fast adaptation based on the detected CCs may enable the use of different basis sequences for the block code.

The number of bits available to send CSI and/or other information may also be determined based on the ACK/NACK bitwidth or the total transport block count. ACK/NACK information, CSI, and/or other information may be multiplexed, and the resultant UCI may be sent on the PUCCH or PUSCH. One PUCCH or one PUSCH can support feedback of both ACK/NACK information and CSI simultaneously, which may be jointly encoded. The available payload for UCI on the PUCCH or PUSCH may be fixed and may be denoted as n_(PAYLOAD). For example, up to 13 information bits may be sent on the PUCCH based on PUCCH format 3.

In one example, the number of bits available to send CSI and/or other information, n_(CSI), is determined based on the ACK/NACK bitwidth or the total transport block count, as follows:

n _(CSI) =n _(PAYLOAD) −n _(HARQ).  Eq (10)

n_(HARQ) in equation (10) may be determined based on the ACK/NACK bitwidth for the configured CCs, the activated CCs, or the detected CCs, or the scheduled CCs. n_(HARQ) in equation (10) may also be determined based on the total transport block count. n_(HARQ) may be determined based on the DAI, if available. n_(HARQ) may also be dependent on whether the ACK/NACK information is ordered or not ordered.

eNB 110 x may control the number of ACK/NACK bits in view of potential feedback overhead for CSI. For example, eNB 110 x may schedule up to five downlink CCs in a subframe if there is only 4-bit wideband CSI feedback to report with the ACK/NACK information. Similarly, eNB 110 x may schedule one or two downlink CCs with 2-bit ACK/NACK feedback in a particular subframe when 11-bit CSI feedback is expected and would be multiplexed with the ACK/NACK information. eNB 110 x may thus schedule a number of downlink CCs such that the total overhead for ACK/NACK feedback and CSI feedback can fit in the available payload for UCI.

Table 5 lists four exemplary designs of sending ACK/NACK information. Each of the four ACK/NACK designs is described in further detail below.

TABLE 5 ACK/NACK Designs ACK/NACK Design Description First No DAI No DAI for downlink CCs. Design CSI not multiplexed with ACK/NACK. Second No DAI No DAI for downlink CCs. Design CSI can be multiplexed with ACK/NACK. Third DAI indicates DAI indicates number of downlink CCs Design number of scheduled in a subframe. scheduled CCs CSI can be multiplexed with ACK/NACK. Fourth DAI identifies DAI indicates number of downlink CCs and Design scheduled CCs identifies the scheduled CCs in a subframe. CSI can be multiplexed with ACK/NACK.

In the first ACK/NACK design, DAI is not used for downlink CCs (but may be used for downlink subframes in TDD as described below). The ACK/NACK bitwidth or the total transport block count for power control of the PUCCH carrying ACK/NACK information may be determined based on detected CCs, e.g., as shown in equation (3) or (8). The ACK/NACK bitwidth or the total transport block count for determining the number of resource elements for sending ACK/NACK information on the PUSCH may be determined based on configured CCs, e.g., as shown in equation (1). When DAI is not available, UE 120 x may be configured to drop CSI when it collides with ACK/NACK information in a subframe and the ACK/NACK information comprises more than two bits. In particular, UE 120 x may not multiplex CSI with ACK/NACK information when DAI is not available and it determines that there are more than two bits of ACK/NACK feedback. If there is only one or two ACK/NACK bits, then ACK/NACK information may be multiplexed with CSI as described in LTE Release 8.

In situations where DAI is not utilized, it is possible to reduce DCI overhead. However, without the additional information about scheduled CCs, there may be errors in determining the ACK/NACK bitwidth, which may result in some errors in determination of transmit power for the PUCCH or the number of resource elements in the PUSCH to send ACK/NACK information. Determining the ACK/NACK bitwidth based on the detected CCs for PUCCH power control and based on the configured CCs for counting resource elements on the PUSCH as described herein may mitigate the impact of such errors.

The second ACK/NACK design also does not utilize DAI but provides for multiplexing ACK/NACK with CSI on the PUCCH or PUSCH. The ACK/NACK bitwidth or the total transport block count for ascertaining the number of bits available to send CSI and/or other information may be determined based on the configured CCs, the activated CCs, or the detected CCs. Allowing CSI to be multiplexed with ACK/NACK information may result in less frequent dropping of CSI, which may improve performance of data transmission.

In the third ACK/NACK design, a DAI may be included in a downlink grant and may indicate the number of downlink CCs scheduled in a subframe, i.e., the total number of PDSCH transmissions. UE 120 x may perform various functions based on the DAI. For example, UE 120 x may determine the ACK/NACK bitwidth based on the DAI, as shown in equation (4) or (5). UE 120 x may then determine the transmit power for sending ACK/NACK information on the PUCCH, the number of resource elements for sending ACK/NACK information on the PUSCH, the ACK/NACK feedback scheme for sending ACK/NACK information, the number of bits available to send CSI and/or other information, the code rate for encoding ACK/NACK information, etc. based on the ACK/NACK bitwidth or the total transport block count. UE 120 x may also utilize the DAI to reduce PDCCH blind detection and lower the associated probability of false alarms. In particular, UE 120 x may utilize explicit information on the number of scheduled CCs obtained from the DAI to determine when to stop decoding the PDCCH and avoid processing downlink CCs that do not include any downlink grants.

In the fourth ACK/NACK design, a DAI may be included in a downlink grant and may indicate both the number of downlink CCs scheduled in a subframe and the identify the scheduled CCs, i.e., the total number and position of the scheduled CCs. CC identity may be signaled, for example, when the bits of the DAI correspond to different ones of the CCs configured for UE 120 x. Using information from the DAI, UE 120 x may perform various functions. For example, UE 120 x may accurately determine the ACK/NACK bitwidth based on the scheduled CCs indicated by the DAI, as shown in equation (7). UE 120 x may also accurately determine the transmit power for sending ACK/NACK information on the PUCCH, the number of resource elements for sending ACK/NACK information on the PUSCH, the ACK/NACK feedback scheme for sending ACK/NACK information, the number of bits available to send CSI and/or other information, the code rate for encoding ACK/NACK information, etc. based on the ACK/NACK bitwidth or the total transport block count. UE 120 x may also utilize the DAI to determine which downlink CCs to decode the PDCCH for downlink grants and which downlink CCs to skip.

Table 6 summarizes transmission of ACK/NACK information on the PUCCH for the three schemes listed in Table 3.

TABLE 6 ACK/NACK Transmission on PUCCH Scheme Description No DAI PUCCH power control based on detected CCs. DAI indicates PUCCH power control based on DAI. number of Some leftover room for multiplexing CSI with scheduled CCs ACK/NACK. Improved PDCCH blind detection and false alarm probability. DAI identifies PUCCH power control based on DAI. scheduled CCs Accurate ACK/NACK bitwidth determination. Maximum leftover room for multiplexing CSI with ACK/NACK. Improved PDCCH blind detection and false alarm probability.

Table 7 summarizes transmission of ACK/NACK information on the PUSCH for the three schemes listed in Table 3.

TABLE 7 ACK/NACK Transmission on PUSCH Scheme Description No DAI Number of resource elements for ACK/NACK information determined based on configured CCs or activated CCs. DAI Number of resource elements for ACK/NACK information indicates determined based on DAI. number of Improved PDCCH blind detection and false alarm probability. scheduled CCs DAI Number of resource elements for ACK/NACK information identifies determined based on DAI. scheduled Accurate ACK/NACK bitwidth determination. CCs Improved PDCCH blind detection and false alarm probability.

UE 120 x may be configured with semi-persistent scheduling (SPS) on the downlink. For SPS, UE 120 x may be semi-statically configured with pertinent parameters for data transmission on a downlink CC, and each PDSCH transmission may occur without sending a downlink grant on the PDCCH. SPS may be supported on only the downlink PCC or on any downlink CC configured for UE 120 x.

When SPS is present (possibly on only the downlink PCC), misalignment between eNB 110 x and UE 120 x may occur even if a DAI is present in downlink grants sent on downlink SCCs. For example, UE 120 x may be configured with two downlink CCs, with CC1 being a PCC and CC2 being an SCC. UE 120 x may be configured for SPS on the PCC without DAI and may be dynamically scheduled on the SCC with DAI. If UE 120 x fails to detect the PDCCH for CC2, it may not know whether there is (i) only an SPS transmission on CC1, or (ii) both an SPS transmission on CC1 and a dynamically scheduled transmission on CC2, or (iii) dynamically scheduled transmissions on both CC1 and CC2 (with the dynamically scheduled transmission on CC1 superseding an SPS transmission).

The situation described above may be addressed in various manners. In one example, UE 120 x may behave as if the DAI is not included in downlink grants. UE 120 x may then perform PUCCH power control based on detected CCs, determine the number of PUSCH resource elements based on configured CCs, etc. In another example, the DAI may include information for the PCC regardless of whether an SPS transmission or a dynamically scheduled transmission is sent on the PCC. In yet another example, the DAI may exclude information for the PCC if it has an SPS transmission and may include information for the PCC if it has a dynamically scheduled transmission. An SPS transmission on the PCC may be associated with a fixed bitwidth (e.g., 1 bit) and a fixed location on the PUCCH or PUSCH if there is no dynamic scheduling transmission on the PCC. Otherwise, the DAI may include information for the PCC if it has a dynamically scheduled transmission. Dynamically scheduled transmission may supersede SPS transmission when they conflict. In each case, UE 120 x may perform PUCCH power control, determine the number of PUSCH resource elements, etc., as described above based on the availability of the DAI (or lack thereof).

In the third scheme shown in Table 3, a DAI may be included in each downlink grant and may identify all scheduled CCs. This arrangement is shown in FIG. 7. With information from the DAI, UE 120 x may obtain knowledge of the scheduled CCs as long as at least one downlink grant is received in a particular subframe. UE 120 x may determine the ACK/NACK bitwidth based on the number of ACK/NACK bits for each scheduled CC, e.g., as shown in equation (7).

It may be desirable for UE 120 x to send DTX to indicate a downlink grant/PDCCH that is not detected by UE 120 x. For example, UE 120 x may determine that CCx is scheduled based on the DAI included with a downlink grant received on CCy. However, UE 120 x may not detect a downlink grant for a PDSCH transmission on CCx. In that case, depending upon its configuration, UE 120 x signals DTX for CCx, and eNB 110 x may use the DTX feedback to improve transmission of the PDCCH for CCx.

Unused bits may be used to convey DTX as follows. A given downlink CC, CCj, may be configured with a transmission mode supporting two transport blocks (e.g., a MIMO mode) and may be associated with two ACK/NACK bits. However, in a particular subframe, CCj may be scheduled with a transmission of one transport block (e.g., a SIMO mode). Only one ACK/NACK bit may needed to acknowledge the transmission on CCj. The unused bit allocated based on the transmission mode may be used to convey whether or not there is a missing downlink grant/PDCCH based upon information from the DAI. Unused bits may also be referred to as leftover bits, orphan bits, etc. Unused bits for multiple downlink CCs may be used jointly to convey more information to eNB 110 x, e.g., to convey which particular downlink grant/PDCCH is not detected by UE 120 x.

In one example of reusing ACK/NACK bits, UE 120 x may be configured with three downlink CCs, which may include CC1, CC2 and CC3. All three configured CCs may be associated with transmission modes supporting two transport blocks, for which two ACK/NACK bits are potentially needed for acknowledging a corresponding PDSCH transmission. eNB 110 x may schedule two of the configured CCs in a given subframe, with CC1 being scheduled with DCI format 1A for one transport block, and CC3 being scheduled with DCI format 2 for two transport blocks. Four ACK/NACK bits may be available for the two scheduled CCs based on their transmission modes. However, for the data transmission described above, only three ACK/NACK bits may be generated, or one ACK/NACK bit for CC1 and two ACK/NACK bits for CC3. In that case, one unused bit would be available to UE 120 x for conveying DTX for one CC. The unused bit may, for example, be used to convey DTX for CC3 and may be set to a first value (e.g., ‘0’) if a downlink grant/PUCCH for CC3 is received, or to a second value (e.g., ‘1’) if the downlink grant/PUCCH for CC3 is not received based on information about scheduled CCs obtained from the DAI. The four ACK/NACK bits may then be sent as follows:

-   -   Send {x100} to inform eNB 110 x that the downlink grant for CC3         is missing, or     -   Send {x0yz} to inform eNB 110 x that the downlink grant for CC3         is detected,         where x is an ACK/NACK bit for CC1, y and z are two ACK/NACK         bits for CC3, and x, y and z may each have a value of ‘0’ or         ‘1’.

In general, 12 bits may be used to convey ACK, NACK, or DTX for five downlink CCs. UE 120 x may be configured to report DTX whenever unused bits are available, or to report DTX upon the occurrence or certain conditions. For example, UE 120 x may report DTX only if the number of configured or scheduled CCs is less than four (in order to fit into a 10-bit ACK/NACK payload), or only if two downlink CCs are configured, etc.

A DAI may also be used to convey information about scheduled subframes in TDD. For example, 2-bit DAI may be included in a downlink grant sent based on DCI format 1, 1A, 1B, 1D, 2, 2A or 2B in LTE. The 2-bit DAI may be sent in subframe n and may indicate the accumulative number of PDCCH(s) with assigned PDSCH transmission(s) and PDCCH indicating SPS release, up to the present subframe within subframe(s) n-k, with k belonging to K, where K denotes a set of downlink subframes associated with the same uplink subframe in which ACK/NACK feedback is sent. The 2-bit DAI may also be included in an uplink grant sent based on DCI format 0 in LTE. In this case, the DAI may be detected by UE 120 x in subframe n-k′ and may represent the total number of subframes with PDSCH transmissions and with PDCCH indicating downlink SPS release within subframes n-k′, with k′ belonging to K. In each case, the DAI may help UE 120 x to detect the missing downlink grants, facilitate more efficient ACK/NACK feedback, and provide other advantages.

In one design, a two-dimensional (2-D) DAI may be used to convey information about scheduled CCs and scheduled subframes for multi-carrier operation in TDD. The 2-D DAI may include two components, DAI_Time and DAI_Freq, to cover time domain and frequency domain, respectively. DAI_Time may be included in a grant when operating in TDD. DAI_Freq may be included in a grant if UE 120 x is configured with two or more downlink CCs in either FDD or TDD. DAI_Time may comprise two bits and may be provided for each downlink CC. DAI_Time may be included in a downlink grant or an uplink grant and may indicate the accumulative number of PDSCH transmissions (in time) over downlink subframes in a downlink subframe association set on a particular downlink CC. DAI_Freq may comprise one to three bits and may be provided for each downlink subframe. DAI_Freq may be included in a downlink grant or an uplink grant and may indicate the total number of scheduled CCs and/or which CCs are scheduled in a given subframe. DAI_Time and/or DAI_Freq may also convey different information dependent on whether they are included in a downlink grant or an uplink grant. For example, DAI_Freq included in a downlink grant may identify the scheduled CCs whereas DAI_Freq included in an uplink grant may indicate the number of scheduled CCs.

In some situations, it is desirable to reduce the number of ACK/NACK bits for transmission on the uplink. The number of bits of ACK/NACK information may be reduced by performing spatial bundling, subframe bundling, and/or CC bundling, as described in Table 8.

TABLE 8 Bundling Bundling Type Description Spatial Bundle ACKs and/or NACKs for transport blocks received via Bundling multiple layers on one downlink CC in one subframe. Subframe Bundle ACKs and/or NACKs for transport blocks received Bundling on one downlink CC in multiple subframes. CC Bundle ACKs and/or NACKs for transport blocks received on Bundling multiple downlink CCs in one subframe.

In general, a UE may utilize one or more types of bundling to reduce the amount of ACK/NACK feedback. Bundling may be performed in different manners depending on various factors such as whether a wireless network utilizes FDD or TDD, the number of configured CCs, the uplink-downlink configuration in TDD, the desired ACK/NACK payload size, channel conditions, etc.

For spatial bundling, multiple transport blocks may be received via multiple layers on one downlink CC in one subframe, and an ACK or a NACK may be obtained for each transport block. A bundled ACK may be generated if ACKs are obtained for all transport blocks. A bundled NACK may be generated if a NACK is obtained for any transport block. For subframe bundling, multiple transport blocks may be received on one downlink CC in multiple subframes, e.g., one transport block in each subframe. An ACK or a NACK may be obtained for each transport block. A bundled ACK may be generated if ACKs are obtained for all transport blocks, and a bundled NACK may be generated if a NACK is obtained for any transport block. For CC bundling, multiple transport blocks may be received on multiple downlink CCs in one subframe, e.g., one transport block one each downlink CC. An ACK or a NACK may be obtained for each transport block. A bundled ACK may be generated if ACKs are obtained for all transport blocks, and a bundled NACK may be generated if a NACK is obtained for any transport block. With all three types of bundling, when eNB 110 x receives a bundled NACK, it may retransmit all of the applicable transport blocks.

In some examples, spatial bundling is utilized with multi-carrier operation in FDD. Up to M ACK/NACK bits may be generated for M configured CCs, e.g., one ACK/NACK bit for each configured CC or scheduled CC. To improve coverage of ACK/NACK transmission, the number of configured CCs may be limited and/or ACK/NACK information may be sent with repetition, e.g., by a factor of 2, 4, or 6. ACK/NACK repetition may be utilized when there is little impact to UCI transmission. For example, since a CSI transmission may be dropped when an ACK/NACK transmission is sent, ACK/NACK repetition may be utilized when CSI transmission is not impacted.

In some examples, spatial bundling and subframe bundling may utilized for multi-carrier operation in TDD. UE 120 x may be configured with (i) up to five downlink CCs for multi-carrier operation and (ii) an uplink-downlink configuration with up to four downlink subframes to one uplink subframe for TDD. One or more ACK/NACK feedback modes may be supported, and each ACK/NACK feedback mode may perform bundling in a different manner.

In a first ACK/NACK feedback mode for multi-carrier operation in TDD, only one type of bundling may be performed, with the bundling type being dependent on the number of configured CCs. If one CC is configured, then only spatial bundling may be performed to obtain up to four ACK/NACK bits, one ACK/NACK bit for each downlink subframe. If two CCs are configured, then only subframe bundling may be performed to obtain up to four ACK/NACK bits, or up to two ACK/NACK bits for each configured CC or scheduled CC. Alternatively, only spatial bundling may be performed to obtain up to eight ACK/NACK bits, or one ACK/NACK bit for each configured CC in each downlink subframe. If three or more CCs are configured, then only subframe bundling may be performed to obtain up to 2*M ACK/NACK bits, or up to two ACK/NACK bits for each configured CC or scheduled CC.

In a second ACK/NACK feedback mode for multi-carrier operation in TDD, one or more types of bundling may be performed, with the bundling type(s) being dependent on the number of configured CCs. If one CC is configured, then only subframe bundling may be performed to obtain up to two ACK/NACK bits. If two CCs are configured, then both spatial bundling and subframe bundling may be performed to obtain up to two ACK/NACK bits. If three or more CCs are configured, then both spatial bundling and subframe bundling may be performed to obtain up to M ACK/NACK bits, e.g., one ACK/NACK bit for each configured CC or scheduled CC.

Bundling may also be performed in other manners. For example, CC bundling may be performed for a subset of the M configured CCs (e.g., downlink CCs with sufficient correlation) instead of all M configured CCs. Subframe bundling may be performed for a subset of all downlink subframes in a radio frame.

The techniques described herein provide various advantages. First, the techniques may facilitate efficient ACK/NACK feedback for multi-carrier operation in FDD and TDD. The techniques may also provide multiplexing capability among different types of UCI, e.g., multiplexing of ACK/NACK and CSI in one subframe. A DAI may cover time domain (for TDD) and/or frequency domain (for FDD). A DAI may also be defined to be causal, so that a DAI sent in subframe n does not cover scheduling in subframes n+1 and later. This may allow independent scheduling to be maintained across downlink subframes in a bundling window.

FIG. 8 shows an exemplary process 800 for sending ACK/NACK information in a multi-carrier wireless network. Process 800 may be performed by a UE (as described below) or by some other entity. The UE may receive a grant on a CC in a plurality of CCs configured for the UE (block 812). The plurality of configured CCs at block 812 may be downlink CCs in a wireless network utilizing FDD, downlink CCs in wireless network utilizing TDD, or a combination thereof.

The UE may be scheduled for a data transmission on at least one scheduled CC in the plurality of configured CCs. The UE may determine the number of scheduled CCs and an identifier of each scheduled CC in the data transmission based on the grant (block 814). The UE may determine ACK/NACK information for the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC (block 816). The UE may send the ACK/NACK information as feedback for the at least one data transmission (block 818).

In one example, the UE may order ACK/NACK bits for the scheduled CCs in the data transmission based on an index of each CC in the plurality of configured CCs, e.g., as illustrated by the ordered case in FIG. 6. In another example, the UE may place ACK/NACK bit(s) for each CC at a specific position assigned to that CC, e.g., as illustrated by the non-ordered case in FIG. 6.

The UE may determine the number of scheduled CCs and the identifier of each scheduled CC by detecting a DAI in the grant. The DAI can provide an explicit indication of which CCs are scheduled in a particular subframe by the UE can determine a corresponding transmission mode, etc. The DAI may have a variable size, which may be determined by the base station based on the number of CCs that are configured for the UE. Alternatively, the DAI may have a fixed size, which may be based on a maximum allowable number of configured CCs.

In one example, the UE may obtain a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC from the grant such as the arrangement shown in FIG. 7. The number of bits of the bitmap may be less than the number of configured CCs for the UE. The plurality of configured CCs may include a first CC and at least one remaining CC. The grant may be for a data transmission on the first CC, and the bitmap may identify each scheduled CC in the at least one remaining CC.

The UE may determine a transmission mode of each scheduled CC based on information obtained from the DAI. The UE may determine a total number of ACK/NACK bits for acknowledging the data transmission based on the transmission mode of each scheduled CC and the number of scheduled CCs. For example, the UE may determine a number of ACK/NACK bits for each scheduled CC individually according to it transmission mode. The UE may then determine the total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC, e.g., as shown in equation (7).

The total number of ACK/NACK bits may be used for various purposes. In one example, the UE may determine a transmit power for sending the ACK/NACK information based on the total number of ACK/NACK bits. The UE may send the ACK/NACK information on a PUCCH based on the determined transmit power. In another example, the UE may determine a number of resource elements for sending the ACK/NACK information based on the total number of ACK/NACK bits. The UE may send the ACK/NACK information on a PUSCH based on the determined number of resource elements.

The UE may determine a PUCCH format, a code rate, and/or a coding scheme for sending the ACK/NACK information based on the total number of ACK/NACK bits. For instance, the UE may select PUCCH format 1 b when the total number of ACK/NACK bits is below a threshold value and PUCCH format 3 when the total exceeds the threshold. The UE may send the ACK/NACK information on the PUCCH based on the determined PUCCH format, a code rate, and/or a coding scheme. The UE may also determine a number of bits for sending CSI based on the total number of ACK/NACK bits and an available payload size. The UE may multiplex the CSI with the ACK/NACK information based on the available bits for sending the CSI.

The UE may determine the number of transport blocks received on each scheduled CC. For example, the UE may determine that (i) one transport block is received on each scheduled CC associated with a downlink grant having a DCI format supporting one transport block and (ii) two transport blocks are received on each scheduled CC associated with a downlink grant having a DCI format supporting two transport blocks. The UE may determine the total number of transport blocks received on the at least one scheduled CC based on the number of transport blocks received on each scheduled CC.

The total number of transport blocks may be used for various purposes. In one design, the UE may determine a transmit power for sending the ACK/NACK information based on the total number of transport blocks received in the data transmission. The UE may send the ACK/NACK information on a PUCCH based on the determined transmit power. Alternatively, when the ACK/NACK information is to be sent on PUSCH, the UE may determine the number of resource elements based on the total number of transport blocks received in the data transmission. The UE may send the ACK/NACK information on a PUSCH based on the determined number of resource elements.

With TDD, the UE may determine a number of downlink subframes in which the UE is scheduled, e.g., based on the grant. The UE may determine ACK/NACK information for data transmission received on the at least one scheduled CC in the determined number of downlink subframes. The ACK/NACK information may be determined based on the number of scheduled CCs, the identifier of each scheduled CC, and the number of downlink subframes in which the UE is scheduled. Additionally, to reduce the amount of ACK/NACK feedback, the UE may perform spatial bundling, subframe bundling, CC bundling, or a combination thereof as previously described.

In one example, the UE may identify at least one unused bit based on (i) the number of bits available to send the ACK/NACK information and (ii) the number of bits to send for the ACK/NACK information. Based on information obtained from the DAI, the UE may send information indicating that a grant is missed for one of the scheduled CCs using the at least one unused bit.

The grant received by the UE in block 812 may be a downlink grant for a data transmission on one of the at least one scheduled CC or an uplink grant for a data transmission on the uplink. In one example, the eNB sends the DAI in separate downlink and uplink grants to reduce the likelihood that the it is missed by the UE. The uplink grant may convey the number of scheduled CCs and the identifier of each scheduled CC for the data transmission on the downlink. The UE may perform blind decoding for PDCCHs carrying grants based on the number of scheduled CCs and the identifier of each scheduled CC.

In one design, information indicative of the number of scheduled CCs and the identifier of each scheduled CC may be sent on only a PCC for the UE, or only a subset of the configured CCs for the UE, or all scheduled CCs for the UE. The PCC may be one of the plurality of configured CCs for the UE.

FIG. 9 shows an exemplary process 900 for receiving ACK/NACK information in a wireless network. Process 900 may be performed by a base station/eNB (as described below) or by some other entity. The base station may generate a grant indicating a number of scheduled CCs and an identifier of each scheduled CC for a data transmission to a UE (block 912). The grant may comprise a bitmap or some other information indicative of the number of CCs scheduled for the data transmission and the identifier of each scheduled CC.

The base station may send the grant on one of a plurality of CCs configured for the UE (block 914). The base station may send the data transmission on at least one scheduled CC to the UE (block 916) and receive ACK/NACK information for the data transmission from the UE (block 918). The ACK/NACK information may be determined by the UE based on the number of scheduled CCs and the identifier of each scheduled CC.

In one design, the ACK/NACK information may be sent by the UE on a PUCCH at a transmit power determined based on the total number of transport blocks received by the UE in the data transmission. In another design, the ACK/NACK information may be sent by the UE on a PUSCH. The base station may determine a transmission mode of CC scheduled for the data transmission and may determine the total number of ACK/NACK bits for the data transmission based on its transmission mode and the number of scheduled CCs. For example, the base station may determine the number of resource elements for acknowledging the data transmission based on the total number of ACK/NACK bits. The base station may receive the ACK/NACK information on a PUSCH based on the determined number of resource elements. Also, the base station may determine a number of bits available for sending CSI based on the total number of ACK/NACK bits and an available payload size. The base station may demultiplex the CSI and the ACK/NACK information the number of available bits.

In one design, the base station may schedule the UE for data transmission in a subframe based on whether reporting of CSI is due from the UE in the subframe. The base station may determine the number of bits of CSI to report by the UE in the subframe. The base station may determine the number of bits available to send ACK/NACK information by the UE in the subframe. The base station may schedule the UE for data transmission in the subframe based on the number of bits available to send ACK/NACK information by the UE, as described above.

FIG. 10 shows a block diagram of a design of a base station/eNB 110 y and a UE 120 y, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. Within base station 110 y, a module 1010 may generate PDCCH transmissions comprising downlink grants and/or other DCI for one or more CCs on which UE 120 y is scheduled. A module 1012 may generate PDSCH transmissions comprising data for the scheduled CCs. A transmitter 1014 may generate and transmit one or more downlink signals comprising the PDCCH and/or PDSCH transmissions. A receiver 1016 may receive and process uplink signals transmitted by UE 120 y and other UEs. A module 1020 may determine transmission parameters (e.g., an ACK/NACK feedback scheme, a code rate, etc.) for ACK/NACK information sent by UE 120 y for data transmission sent by eNB 110 y. A module 1018 may process one or more received signals in accordance with the ACK/NACK transmission parameters to recover the ACK/NACK information sent by UE 120 y. Module 1018 may also recover CSI and/or other information sent by UE 120 y.

A module 1022 may determine a multi-carrier configuration of UE 120 y, e.g., determine which CCs are configured for UE 120 y for the downlink and uplink, and which CCs are downlink PCC and uplink PCC for UE 120 y. A module 1024 may determine the ACK/NACK bitwidth and/or the total transport block count for UE 120 y based on various factors such as whether or not DAI is included in grants sent to UE 120 y, the configured CCs or scheduled CCs for UE 120 y, whether bundling is performed, etc. A module 1026 may determine the number of resource elements used by UE 120 y to send ACK/NACK information on the PUSCH. The various modules within base station 110 y may operate as described above. A controller/processor 1028 may direct the operation of various modules within base station 110 y. A memory 1030 may store data and program codes for base station 110 y. A scheduler 1032 may schedule UEs for data transmission.

Within UE 120 y, a receiver 1050 may receive and process downlink signals from base station 110 y and other base stations. A module 1052 may process (e.g., demodulate and decode) one or more received signals to recover PDCCH transmissions sent to UE 120 y. A module 1054 may process the received signal to recover PDSCH transmissions sent to UE 120 y. A module 1058 may determine ACK/NACK information for received data transmission. A module 1056 may determine transmission parameters for sending the ACK/NACK information. Module 1058 may send the ACK/NACK information on the PUCCH or PUSCH in accordance with the ACK/NACK transmission parameters. Module 1058 may also send CSI and/or other information on the PUCCH or PUSCH. A transmitter 1060 may generate and transmit one or more uplink signals comprising a PUCCH transmission or a PUSCH transmission.

A module 1068 may determine a multi-carrier configuration of UE 120 y, e.g., determine which CCs are configured for UE 120 y for the downlink and uplink, and which CCs are downlink PCC and uplink PCC for UE 120 y. A module 1062 may determine the ACK/NACK bitwidth and/or the total transport block count for UE 120 y based on various factors such as whether or not DAI is included in grants sent to UE 120 y, the configured CCs or scheduled CCs for UE 120 y, whether bundling is performed, etc. A module 1064 may perform power control for the PUCCH based on the ACK/NACK bitwidth and/or the total transport block count, e.g., determine the transmit power for sending the ACK/NACK information on the PUCCH. A module 1066 may determine the number of resource elements for sending the ACK/NACK information on the PUSCH. The various modules within UE 120 y may operate as described above. A controller/processor 1070 may direct the operation of various modules within UE 120 y. A memory 1072 may store data and program codes for UE 120 y.

The modules in FIG. 10 may comprise processors, electronic devices, hardware devices, electronic components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

FIG. 11 shows a block diagram of a design of a base station/eNB 110 z and a UE 120 z, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. Base station 110 z may be equipped with T antennas 1134 a through 1134 t, and UE 120 z may be equipped with R antennas 1152 a through 1152 r, where in general T≧1 and R≧1.

At base station 110 z, a transmit processor 1120 may receive data from a data source 1112 for transmission on one or more downlink CCs to one or more UEs, process (e.g., encode and modulate) the data for each UE based on one or more modulation and coding schemes selected for that UE, and provide data symbols for all UEs. Transmit processor 1120 may also process control information (e.g., for grants, DAI, configuration messages, etc.) and provide control symbols. Processor 1120 may also generate reference symbols for reference signals. A transmit (TX) MIMO processor 1130 may precode the data symbols, the control symbols, and/or the reference symbols (if applicable) and may provide T output symbol streams to T modulators (MOD) 1132 a through 1132 t. Each modulator 1132 may process its output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 1132 may further condition (e.g., convert to analog, amplify, filter, and upconvert) its output sample stream to obtain a downlink signal. T downlink signals from modulators 1132 a through 1132 t may be transmitted via T antennas 1134 a through 1134 t, respectively.

At UE 120 z, antennas 1152 a through 1152 r may receive the downlink signals from base station 110 z and/or other base stations and may provide received signals to demodulators (DEMODs) 1154 a through 1154 r, respectively. Each demodulator 1154 may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain input samples. Each demodulator 1154 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 1156 may obtain received symbols from all R demodulators 1154 a through 1154 r, perform MIMO detection on the received symbols, and provide detected symbols. A receive processor 1158 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120 z to a data sink 1160, and provide decoded control information to a controller/processor 1180.

On the uplink, at UE 120 z, a transmit processor 1164 may receive and process data from a data source 1162 and control information (e.g., ACK/NACK information, CSI, etc.) from controller/processor 1180. Processor 1164 may also generate reference symbols for one or more reference signals. The symbols from transmit processor 1164 may be precoded by a TX MIMO processor 1166 if applicable, further processed by modulators 1154 a through 1154 r (e.g., for SC-FDM, OFDM, etc.), and transmitted to base station 110 z. At base station 110 z, the uplink signals from UE 120 z and other UEs may be received by antennas 1134, processed by demodulators 1132, detected by a MIMO detector 1136 if applicable, and further processed by a receive processor 1138 to obtain decoded data and control information sent by UE 120 z and other UEs. Processor 1138 may provide the decoded data to a data sink 1139 and the decoded control information to controller/processor 1140.

Controllers/processors 1140 and 1180 may direct the operation at base station 110 z and UE 120 z, respectively. Processor 1140 and/or other processors and modules at base station 110 z may perform or direct process 900 in FIG. 9 and/or other processes for the techniques described herein. Processor 1180 and/or other processors and modules at UE 120 z may perform or direct process 800 in FIG. 8 and/or other processes for the techniques described herein. Memories 1142 and 1182 may store data and program codes for base station 110 z and UE 120 z, respectively. A scheduler 1144 may schedule UEs for data transmission on the downlink and/or uplink.

It will be recognized that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Also, it will be appreciated that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), then the coaxial cable, fiber optic cable, twisted pair, or DSL are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

What is claimed is:
 1. A method for wireless communication, comprising: receiving a grant on a component carrier (CC) in a plurality of CCs configured for a user equipment (UE); determining, based on the grant, a number of scheduled CCs and an identifier of each scheduled CC for the UE; and determining acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC.
 2. The method of claim 1, further comprising: determining a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks received on the scheduled CC, and determining a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 3. The method of claim 1, further comprising: determining a transmit power for sending the ACK/NACK information based on a total number of ACK/NACK bits for the at least one scheduled CC; and sending the ACK/NACK information on a physical uplink control channel (PUCCH) based on the determined transmit power.
 4. The method of claim 1, further comprising: determining a number of resource elements for sending the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission; and sending the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the number of resource elements.
 5. The method of claim 1, further comprising: determining a physical uplink control channel (PUCCH) format for sending the ACK/NACK information based on a total number of ACK/NACK bits for data transmission; and sending the ACK/NACK information on the PUCCH based with the PUCCH format.
 6. The method of claim 1, further comprising: determining available bits for sending channel state information (CSI) based on a total number of ACK/NACK bits for the data transmission and an available payload size; and multiplexing the CSI with the ACK/NACK information based on a number of the available bits.
 7. The method of claim 1, further comprising: determining a number of transport blocks received on each scheduled CC; and determining a total number of transport blocks received in the data transmission based on the number of transport blocks received on each scheduled CC.
 8. The method of claim 7, wherein the determining the number of transport blocks received on each scheduled CC comprises: determining that one transport block is received on each scheduled CC associated with a downlink grant having a downlink control information (DCI) format supporting one transport block, and determining that two transport blocks are received on each scheduled CC associated with a downlink grant having a DCI format supporting two transport blocks.
 9. The method of claim 1, further comprising: determining a transmit power for sending the ACK/NACK information based on a total number of transport blocks received in the data transmission; and sending the ACK/NACK information on a physical uplink control channel (PUCCH) based on the determined transmit power.
 10. The method of claim 1, further comprising: ordering ACK/NACK bits for the at least one scheduled CC based on an index of each CC in the plurality of configured CCs.
 11. The method of claim 1, wherein the determining the number of scheduled CCs and the identifier of each scheduled CC comprises detecting a downlink assignment indicator (DAI) in the grant.
 12. The method of claim 11, wherein a size of the DAI is based on a number of configured CCs for the UE.
 13. The method of claim 1, wherein determining the number of scheduled CCs and the identifier of each scheduled CC comprises: obtaining, from the grant, a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 14. The method of claim 13, wherein a number of bits of the bitmap is less than a number of configured CCs for the UE.
 15. The method of claim 13, wherein the plurality of configured CCs comprise a first CC and at least one remaining CC, wherein the grant is for a data transmission on the first CC, and wherein the bitmap identifies each scheduled CC in the at least one remaining CC.
 16. The method of claim 1, further comprising: determining a number of downlink subframes in which the UE is scheduled based on the grant; and determining ACK/NACK information for data transmissions received on the at least one scheduled CC in the determined number of downlink subframes, wherein the ACK/NACK information is determined based on the number of scheduled CCs, the identifier of each scheduled CC, and the number of downlink subframes in which the UE is scheduled.
 17. The method of claim 1, wherein determining the ACK/NACK information comprises: performing spatial bundling, subframe bundling, CC bundling, or a combination thereof to obtain the ACK/NACK information.
 18. The method of claim 1, further comprising: identifying at least one unused bit based on a number of bits available to send the ACK/NACK information and a number of bits of the ACK/NACK information to send; and sending information indicating that a grant for one of the scheduled CCs is missed by the UE using the at least one unused bit.
 19. The method of claim 1, further comprising: detecting physical downlink control channels (PDCCHs) with grants based on the number of scheduled CCs and the identifier of each scheduled CC.
 20. The method of claim 1, wherein the grant comprises a downlink grant for a data transmission on one of the at least one scheduled CC or an uplink grant for a data transmission on an uplink.
 21. The method of claim 1, wherein the plurality of configured CCs are downlink CCs in a wireless network utilizing frequency division duplexing (FDD).
 22. The method of claim 1, wherein information indicative of the number of scheduled CCs and the identifier of each scheduled CC is received on a primary CC (PCC) for the UE, the PCC being one of the plurality of configured CCs for the UE.
 23. The method of claim 1, wherein information indicative of the number of scheduled CCs and the identifier of each scheduled CC is received on a subset of the plurality of configured CCs for the UE.
 24. An apparatus for wireless communication, comprising: means for receiving a grant on a component carrier (CC) in a plurality of CCs configured for a user equipment (UE); means for determining, based on the grant, a number of scheduled CCs and an identifier of each scheduled CC for the UE; and means for determining acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC.
 25. The apparatus of claim 24, further comprising: means for determining a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks received on the scheduled CC, and means for determining a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 26. The apparatus of claim 24, further comprising: means for determining a transmit power for sending the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission; and means for sending the ACK/NACK information on a physical uplink control channel (PUCCH) based on the determined transmit power.
 27. The apparatus of claim 24, further comprising: means for determining a number of resource elements for sending the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission; and means for sending the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the determined number of resource elements.
 28. The apparatus of claim 24, wherein the means for determining the number of scheduled CCs and the identifier of each scheduled CC comprises: means for detecting a downlink assignment indicator (DAI) in the grant.
 29. The apparatus of claim 24, wherein the means for determining the number of scheduled CCs and the identifier of each scheduled CC comprises: means for obtaining, from the grant, a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 30. The apparatus of claim 24, wherein the means for determining the ACK/NACK information comprises: means for performing spatial bundling, subframe bundling, CC bundling, or a combination thereof to obtain the ACK/NACK information.
 31. An apparatus for wireless communication, comprising: at least one processor configured to: receive a grant on a component carrier (CC) in a plurality of CCs configured for a user equipment (UE), determine, based on the grant, a number of scheduled CCs and an identifier of each scheduled CC for the UE, and determine acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC; and a memory coupled to the at least one processor.
 32. The apparatus of claim 31, wherein the at least one processor is configured to: determine a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks received on the scheduled CC, and determine a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 33. The apparatus of claim 31, wherein the at least one processor is configured to: determine a transmit power for sending the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission, and send the ACK/NACK information on a physical uplink control channel (PUCCH) based on the determined transmit power.
 34. The apparatus of claim 31, wherein the at least one processor is configured to: determine a number of resource elements for sending the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission, and send the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the determined number of resource elements.
 35. The apparatus of claim 31, wherein the at least one processor is configured to detect a downlink assignment indicator (DAI) in the grant.
 36. The apparatus of claim 31, wherein the at least one processor is configured to obtain, from the grant, a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 37. The apparatus of claim 31, wherein the at least one processor is configured to perform spatial bundling, subframe bundling, CC bundling, or a combination thereof to obtain the ACK/NACK information.
 38. A computer program product, comprising: a non-transitory computer-readable medium comprising: code for causing at least one processor to receive a grant on a component carrier (CC) in a plurality of CCs configured for a user equipment (UE), code for causing the at least one processor to determine, based on the grant, a number of scheduled CCs and an identifier of each scheduled CC for the UE, and code for causing the at least one processor to determine acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission based on the number of scheduled CCs and the identifier of each scheduled CC.
 39. A method for wireless communication, comprising: generating a grant indicating a number of scheduled component carriers (CCs) and an identifier of each scheduled CC for a user equipment (UE); sending the grant on one of a plurality of CCs configured for the UE; sending a data transmission to the UE on the scheduled CCs; and receiving acknowledgement/negative acknowledgement (ACK/NACK) information from the UE in response to the grant.
 40. The method of claim 39, further comprising: determining a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks sent on the scheduled CC, and determining a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 41. The method of claim 39, further comprising: determining a number of resource elements used to send the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission; and receiving the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the determined number of resource elements.
 42. The method of claim 39, further comprising: determining available bits for sending channel state information (CSI) based on a total number of ACK/NACK bits for the data transmission and an available payload size; and demultiplexing the CSI and the ACK/NACK information based on the available bits for sending the CSI.
 43. The method of claim 39, wherein the ACK/NACK information is received from the UE on a physical uplink control channel (PUCCH) at a transmit power corresponding to a total number of transport blocks received by the UE in the data transmission.
 44. The method of claim 39, wherein the generating the grant comprises: generating the grant comprising a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 45. The method of claim 39, further comprising: scheduling the UE for data transmission in a subframe based on whether reporting of channel state information (CSI) is due from the UE in the subframe.
 46. The method of claim 39, further comprising: determining a number of bits of channel state information (CSI) for reporting by the UE in a subframe; determining a number of bits available to the UE for sending ACK/NACK information in the subframe based on the number of bits of CSI; and scheduling the UE for data transmission in the subframe based on the number of bits available to send ACK/NACK information.
 47. An apparatus for wireless communication, comprising: means for generating a grant indicating a number of scheduled component carriers (CCs) and an identifier of each scheduled CC for a user equipment (UE); means for sending the grant on one of a plurality of CCs configured for the UE; means for sending a data transmission to the UE on the scheduled CCs; and means for receiving acknowledgement/negative acknowledgement (ACK/NACK) information from the UE in response to the grant.
 48. The apparatus of claim 47, further comprising: means for determining a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks sent on the scheduled CC, and means for determining a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 49. The apparatus of claim 47, further comprising: means for determining a number of resource elements comprising the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission; and means for receiving the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the number of resource elements.
 50. The apparatus of claim 47, further comprising: means for determining available bits for sending channel state information (CSI) based on a total number of ACK/NACK bits for the data transmission and an available payload size; and means for demultiplexing the CSI and the ACK/NACK information based on a number of the available bits.
 51. The apparatus of claim 47, wherein the means for generating the grant comprises: means for generating the grant comprising a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 52. An apparatus for wireless communication, comprising: at least one processor configured to: generate a grant indicating a number of scheduled component carriers (CCs) and an identifier of each scheduled CC for a user equipment (UE), send the grant on one of a plurality of CCs configured for the UE, send a data transmission to the UE on the scheduled CCs, and receive acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission from the UE in response to the grant; and a memory coupled to the at least one processor.
 53. The apparatus of claim 52, wherein the at least one processor is configured to: determine a number of ACK/NACK bits for each scheduled CC based on a transmission mode of the scheduled CC or a number of transport blocks sent on the scheduled CC, and determine a total number of ACK/NACK bits for the data transmission based on the number of ACK/NACK bits for each scheduled CC.
 54. The apparatus of claim 52, wherein the at least one processor is configured to: determine a number of resource elements comprising the ACK/NACK information based on a total number of ACK/NACK bits for the data transmission, and receive the ACK/NACK information on a physical uplink shared channel (PUSCH) based on the number of resource elements.
 55. The apparatus of claim 52, wherein the at least one processor is configured to: determine available bits for sending channel state information (CSI) based on a total number of ACK/NACK bits for the data transmission and an available payload size, and demultiplex the CSI and the ACK/NACK information based on a number of the available bits.
 56. The apparatus of claim 52, wherein the at least one processor is configured to generate the grant comprising a bitmap indicative of the number of scheduled CCs and the identifier of each scheduled CC.
 57. A computer program product, comprising: a non-transitory computer-readable medium comprising: code for causing at least one processor to generate a grant indicating a number of scheduled component carriers (CCs) and an identifier of each scheduled CC for a user equipment (UE), code for causing the at least one processor to send the grant on one of a plurality of CCs configured for the UE, code for causing the at least one processor to send a data transmission to the UE on the scheduled CCs, and code for causing the at least one processor to receive acknowledgement/negative acknowledgement (ACK/NACK) information from the UE in response to the grant. 